The utilisation of overmoulded timepiece components is often advantageous in terms of reduced production costs for large scale manufacturing. Further, the inertia of the components is lower than that of metal components with the same geometry, which is favourable for the overall efficiency of the movement. Overmoulding is generally used for wheels or wheel sets, on and around a metal arbor having one or more shoulders which are left clear to cooperate with pivots or suchlike.
However, the plastic materials chosen for their tribological qualities and for their adherence to their metal frame, most usually an arbor, have the drawback of creep/expansion. This causes problems of serviceability, and leads to a loss of geometry of the toothing(s) of the wheels or pinions manufactured in this manner.
EP Patent Application No 0369704A2 in the name of SHIOJIRI KOGYO discloses a stepped arbor with a one-piece flange, and a plastic toothing at the periphery of the arbor and notably moulded thereon. FR Patent Application No 2020572A1 in the name of WITTNER discloses a metronome escapement wheel moulded in one piece of plastic material with a barrel and its wheel, and particularly onto a notched groove of an arbor. U.S. Pat. No. 3,930,362A in the name of CIELASZYK discloses a wheel whose plate and toothing are made of plastic material overmoulded onto an arbor, to the right of a groove therein.